<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .demo{
            background-color: pink;
        }
    </style>
</head>
<body>
    <button id="btn">点我创建一个输入框</button>
    <script type="text/javascript">
        const btn=document.getElementById('btn')
        btn.onclick = ()=>{
            const input=document.createElement('input')
            input.className='demo'
            input.value=10
            document.body.appendChild(input)
            input.focus()
            input.parentElement.style.backgroundColor='skyblue'
        }
    </script>
</body>
</html>